Epoxy resin

ABSTRACT

Compositions containing: (a) a liquid epoxy resin; (b) an aliphatic or cycloaliphatic primary monoamine and/or an aliphatic or cycloaliphatic disecondary diamine; (c) a latent curing agent for the epoxy resin (a) which does not react until temperatures above 70° C. (measured by means of DSC at a heating rate of 10° C./min); (d) a photopolymerizable compound; and (e) a photoinitiator; the ratio of the number of equivalents of epoxy groups to that of photopolymerizable groups being 1:0.01 to 1:0.7, are suitable as impregnating resins.

The present invention relates to a curable composition containing anepoxy resin and a photopolymerizable compound, and a process for thepreparation of prepregs.

It is known that epoxy resin mixtures with two curing agents ofdifferent reactivity can be used for preparing prepregs having a longshelf life, the B-stage formation (reaction with the reactive curingagent) being effected at room temperature or temperatures <60° C. Thecuring of the prepregs (C-stage formation) is effected by reaction withthe heat-activatable curing agent (latent curing agent) attemperatures >80° C.

According to U.S. Pat. No. 4,608,300, prepregs which have limitedstorability but can be completely cured below 120° C. are obtained byimpregnating fibre materials with liquid, solvent-free epoxy resinsystems containing a mixture of specific aliphatic or cycloaliphaticamines.

U.S. Pat. No. 4,666,954 describes impregnating resins which contain aphotopolymerizable compound and a corresponding photopolymerizationcatalyst in addition to a heat-curable epoxy resin and a latent curingagent. Prepregs which require only short curing times at relatively lowtemperatures can be prepared from these resins.

In the case of highly reactive resins, the B-stage formation is effectedat low temperatures, as a rule between room temperature and 40° C. Atthese temperatures, the viscosity of the resin mixture is oftenrelatively high, which leads to problems with the impregnation of thefibre material.

It has now been found that specific epoxy resin/acrylate compositionshave a high reactivity and a low impregnation viscosity. The prepregsprepared therefrom have a long shelf life at room temperature and can becured in a short time at 100–130° C.

The present invention relates to a composition containing

-   (a) a liquid epoxy resin,-   (b) an aliphatic or cycloaliphatic primary monoamine and/or an    aliphatic or cycloaliphatic disecondary diamine,-   (c) a latent curing agent for the epoxy resin (a) which does not    react until temperatures above 70° C. (measured by means of DSC at a    heating rate of 10° C./min),-   (d) a photopolymerizable compound and-   (e) a photoinitiator,    the ratio of the number of equivalents of epoxy groups to that of    photopolymerizable groups being 1:0.01 to 1:0.7.

In principle, all epoxy resins which are customary in epoxy resintechnology and are liquid at room temperature can be used as component(a). It is also possible to use a mixture of epoxy resins said mixturebeing liquid at room temperature. In the context of the presentinvention, room temperature means a temperature of 20 to 25° C.

Examples of epoxy resins are:

I) Polyglycidyl and poly(β-methylglycidyl) esters, obtainable byreacting a compound having at least two carboxyl groups in the moleculeand, respectively, epichlorohydrin and β-methylepichlorohydrin. Thereaction is expediently effected in the presence of bases.

Aliphatic polycarboxylic acids can be used as the compound having atleast two carboxyl groups in the molecule. Examples of suchpolycarboxylic acids are oxalic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid or dimerized ortrimerized linoleic acid.

However, cycloaliphatic polycarboxylic acids, such as, for example,tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid,hexahydrophthalic acid or 4-methylhexahydrophthalic acid, may also beused.

Furthermore, aromatic polycarboxylic acids, such as, for example,phthalic acid, isophthalic acid or terephthalic acid, may be used.

II) Polyglycidyl or poly(β-methylglycidyl) ethers, obtainable byreacting a compound having at least two free alcoholic hydroxyl groupsand/or phenolic hydroxyl groups with epichlorohydrin orβ-methylepichlorohydrin under alkaline conditions or in the presence ofan acidic catalyst with subsequent treatment with alkali.

The glycidyl ethers of this type are derived, for example, from acyclicalcohols, for example from ethylene glycol, diethylene glycol or higherpoly(oxyethylene) glycols, propane-1,2-diol or poly(oxypropylene)glycols, propane-1,3-diol, butane-1,4-diol, poly(oxytetramethylene)glycols, pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol,glycerol, 1,1,1-trimethylolpropane, pentaerythritol or sorbitol, andfrom polyepichlorohydrins.

Further glycidyl ethers of this type are derived from cycloaliphaticalcohols, such as 1,4-cyclohexanedimethanol,bis(4-hydroxycyclohexyl)methane or 2,2-bis(4-hydroxycyclohexyl)propane,or from alcohols which contain aromatic groups and/or further functionalgroups, such as N,N-bis(2-hydroxyethyl)aniline orp,p′-bis(2-hydroxyethylamino)-diphenylmethane.

The glycidyl ethers may also be based on mononuclear phenols, such as,for example, resorcinol or hydroquinone, or on polynuclear phenols, suchas, for example, bis(4-hydroxyphenyl)methane, 4,4′-dihydroxybiphenyl,bis(4-hydroxyphenyl) sulphone, 1,1,2,2-tetrakis (4-hydroxyphenyl)ethane,2,2-bis(4-hydroxyphenyl)propane or2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane.

Further suitable hydroxy compounds for the preparation of glycidylethers are novolaks, obtainable by condensation of aldehydes, such asformaldehyde, acetaldehyde, chloral or furfuraldehyde, with phenols orbisphenols which are unsubstituted or substituted by chlorine atoms orC₁-C₉-alkyl groups, such as, for example, phenol, 4-chlorophenol,2-methylphenol or 4-tert-butylphenol.

III) Poly(N-glycidyl) compounds, obtainable by dehydrochlorination ofthe reaction products of epichlorohydrin with amines which contain atleast two amine hydrogen atoms. These amines are, for example, aniline,n-butylamine, bis(4-aminophenyl)methane, m-xylylenediamine orbis(4-methylaminophenyl)methane.

However, the poly(N-glycidyl) compounds also include triglycidylisocyanurate, N,N′-diglycidyl derivatives of cycloalkyleneureas, such asethyleneurea or 1,3-propyleneurea, and diglycidyl derivatives ofhydantoins, such as of 5,5-dimethylhydantoin.

IV) Poly(S-glycidyl) compounds, for example di-S-glycidyl derivatives,which are derived from dithiols, such as, for example,ethane-1,2-dithiol or bis(4-mercaptomethylphenyl) ether.

V) Cycloaliphatic epoxy resins, such as, for example,bis(2,3-epoxycyclopentyl) ether, 2,3-epoxycyclopentyl glycidyl ether,1,2-bis(2,3-epoxycyclopentyloxy)ethane or 3,4-epoxycyclohexylmethyl3′,4′-epoxycyclohexanecarboxylate.

However, it is also possible to use epoxy resins in which the 1,2-epoxygroups are bonded to different hetero atoms or functional groups; thesecompounds include, for example, the N,N,O-triglycidyl derivative of4-aminophenol, the glycidyl ether-glycidyl ester of salicylic acid,N-glycidyl-N′-(2-glycidyloxypropyl)-5,5-dimethylhydantoin or2-glycidyloxy-1,3-bis(5,5-dimethyl-1-glycidylhydantoin-3-yl)propane.

Bisphenol diglycidyl ether or an epoxy novolak is preferably used ascomponent (a).

Bisphenol A diglycidyl ether or epoxycresol novolaks are particularlypreferred.

The primary monoamines and disecondary diamines suitable as component(b) are known and some of them are commercially available.

Suitable primary monoamines are, for example, benzylamine,cyclohexylamine, ethanolamine, 2-ethylhexylamine, 2-butoxyethylamine,n-octylamine, 2-phenylethylamine, 3-isopropoxypropylamine,3-amino-2,2-dimethyl-propan-1-ol, 3-(2-ethylhexyloxy)propylamine or2-(2-aminoethoxy)ethanol.

Preferred primary monoamines are benzylamine, n-octylamine,2-phenylethylamine, 3-(2-ethylhexoxy)propylamine and2-(2-aminoethoxy)ethanol.

Examples of disecondary diamines are piperazine,N,N′-dicyclohexyl-1,6-hexamethylenediamine andN,N′-bis(β-cyanoethyl)-1,6-hexamethylenediamine.

In principle, any compound which is known for this purpose and complieswith the definition according to the invention can be used as latentcuring agent (c), i.e. any compound which is inert with respect to theepoxy resin below the defined limiting temperature of 70° C. (measuredby means of DSC at a heating rate of 10° C./min), but which reactsrapidly with crosslinking of the resin as soon as this limitingtemperature is exceeded. The limiting temperature of the latent curingagents used according to the invention is preferably at least 85° C., inparticular at least 100° C. Such compounds are well known and alsocommercially available.

Examples of suitable latent curing agents are dicyandiamide,cyanoguanidines, such as, for example, the compounds described in U.S.Pat. No. 4,859,761 or EP-A 306 451, aromatic amines, such as, forexample, 4,4′- or 3,3′-diaminodiphenyl sulphone, or guanidines, such as,for example, 1-o-tolylbiguanide, or modified polyamines, such as, forexample, Ancamine® 2014 S (Anchor Chemical UK Limited, Manchester).

Other suitable latent curing agents are N-acylimidazoles, such as, forexample, 1-(2′,4′,6′-trimethylbenzoyl)-2-phenylimidazole or1-benzoyl-2-isopropylimidazole. Such compounds are described, forexample, in U.S. Pat. No. 4,436,892, U.S. Pat. No. 4,587,311 or JapanesePatent 743,212.

Further suitable curing agents are metal salt complexes of imidazoles,as described, for example, in U.S. Pat. No. 3,678,007 or U.S. Pat. No.3,677,978, carboxylic acid hydrazides, such as, for example, adipic aciddihydrazide, isophthalic acid dihydrazide or anthranilic acid hydrazide,triazine derivatives, such as, for example,2-phenyl-4,6-diamino-s-triazine (benzoguanamine) or2-lauryl-4,6-diamino-s-triazine (lauroguanamine), and melamine and itsderivatives. The last-mentioned compounds are described, for example, inU.S. Pat. No. 3,030,247.

Other suitable latent curing agents are cyanoacetyl compounds, asdescribed, for example, in U.S. Pat. No. 4,283,520, for exampleneopentylglycol biscyanoacetate, N-isobutylcyanoacetamide,1,6-hexamethylene biscyanoacetate or 1,4-cyclohexanedimethanolbiscyanoacetate.

Other suitable latent curing agents are N-cyanoacylamide compounds, suchas, for example, N,N′-dicyanoadipamide. Such compounds are described,for example, in U.S. Pat. No. 4,529,821, U.S. Pat. No. 4,550,203 andU.S. Pat. No. 4,618,712.

Further suitable latent curing agents are the acylthiopropylphenolsdescribed in U.S. Pat. No. 4,694,096 and the urea derivatives disclosedin U.S. Pat. No. 3,386,955, such as, for example,toluene-2,4-bis(N,N-dimethylcarbamide).

Further suitable latent curing agents are also imidazoles, such as, forexample, imidazole, 2-ethylimidazole, 2-phenylimidazole,1-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole or2-ethyl-4-methylimidazole.

Further suitable latent curing agents are also tertiary amines, such asbenzyldimethylamine or 2,4,6-tris(dimethylaminomethyl)phenol.

Preferred latent curing agents are diaminodiphenyl sulphone,dicyandiamide, phenylimidazole and2,4,6-tris(dimethylaminomethyl)phenol.

If expedient, the mixtures according to the invention may also containaccelerators for the crosslinking reaction with the latent curing agent.Suitable accelerators are, for example, urea derivatives, such asN,N-dimethyl-N′-(3-chloro-4-methylphenyl)-urea (chlortoluron),N,N-dimethyl-N′-(4-chlorophenyl)urea (monuron) orN,N-dimethyl-N′-(3,4-dichlorophenyl)urea (diuron),2,4-bis(N′,N′-dimethylureido)toluene or1,4-bis(N′,N′-dimethylureido)benzene. The use of these compounds isdescribed, for example, in the abovementioned U.S. Pat. No. 4,283,520.Suitable accelerators are, for example, also the urea derivativesdescribed in GB 1,192,790.

Other suitable accelerators are imidazoles, such as, for example,imidazole, 2-ethylimidazole, 2-phenylimidazole, 1-methylimidazole,1-cyanoethyl-2-ethyl-4-methylimidazole or 2-ethyl-4-methylimidazole.

Further suitable accelerators are also tertiary amines, their salts orquaternary ammonium compounds, such as benzyldimethylamine,2,4,6-tris(dimethylaminomethyl)phenol, 4-aminopyridine,tripentylammonium phenolate, tetramethylammonium chloride orbenzyltributylammonium bromide or chloride; or alkali metal alcoholates,such as sodium alcoholates of 2,4-dihydroxy-3-hydroxy-methylpentane.

Other suitable accelerators are the solid solutions of a nitrogen baseand a phenol/aldehyde resin, as described in EP-A 200678, and theMannich bases of polymeric phenols, disclosed in EP-A 351365.

Preferred accelerators are imidazoles and urea derivatives.

Suitable photopolymerizable compounds (d) are in particular acrylic acidesters and methacrylic acid esters, for example the compounds mentionedin U.S. Pat. No. 4,666,954. Preferred components (d) are ethylene glycoldimethacrylate, 1,4-butanediol dimethacrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropyl methacrylate, 2-ethoxyethyl methacrylate,1,1,1-trimethylolpropane trimethacrylate, pentaerythritol tetraacrylateand dipentaerythritol pentacrylate.

In the compositions according to the invention, all types ofphotoinitiators which form free radicals on appropriate irradiation canbe used. Typical known photoinitiators are benzoins, such as benzoin, orbenzoin ethers, e.g. benzoin methyl ether, benzoin ethyl ether, benzoinisopropyl ether or benzoin phenyl ether, and benzoin acetate,acetophenones, such as acetophenone, 2,2-dimethoxyacetophenone and1,1-dichloroacetophenone, benzil, benzil ketals, such as benzil dimethylketal and benzil diethyl ketal, anthraquinones, such as2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone,1-chloroanthraquinone and 2-amylanthraquinone, triphenylphosphine,benzoylphosphine oxides, such as, for example,2,4,6-trimethylbenzoyldiphenylphosphine oxide (Luzirin® TPO),benzophenones, such as benzophenone and4,4-bis(N,N′-dimethylamino)benzophenone, xanthones and thioxanthones,acridine derivatives, phenazine derivatives, quinoxaline derivatives,1-phenyi-1,2-propanedione-2-O-benzoyl oxime,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,1-aminophenyl ketones or 1-hydroxyphenyl ketones, such as1-hydroxycyclohexyl phenyl ketone, phenyl 1-hydroxyisopropyl ketone and4-isopropylphenyl 1-hydroxyisopropyl ketone.

Another class of photoinitiators which is usually employed when argonion lasers are used are the benzil ketals, such as, for example, benzildimethyl ketal.

Preferred photoinitiators (e) are isopropylthioxanthone and2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one.

The photoinitiators are used in effective amounts, i.e. in amounts ofabout 0.01–10.0% by weight, in particular 0.1–5.0% by weight, based onthe total amount of the mixture.

The ratios of the components of the mixtures according to the inventionmay vary considerably depending on the specific composition. Suitableamounts of the latent curing agent are, for example, in the range ofabout 3–60, preferably about 6–30, parts by weight per 100 parts byweight of the epoxy resin.

Compositions according to the invention which contain 0.25–0.75, inparticular 0.40–0.60, aminehydrogen equivalents of the component (b) perepoxide equivalent of the epoxy resin (a) are preferred.

The component (d) is preferably used in amounts, based on the amount ofthe component (a), such that the ratio of the number of equivalents ofepoxy groups to that of photopolymerizable groups is 1:0.05 to 1:0.5, inparticular 1:0.1 to 1:0.4.

The mixtures according to the invention may also be processed from asolution, for example in methyl ethyl ketone, the temperature for theB-stage and the C-stage curing not changing.

If desired, reactive diluents, such as, for example, butanedioldiglycidyl ether, monoglycidyl ethers of isomeric higher alcohols, suchas, for example, Grilonit V1814® from Ems-Chemie, or butyl glycidylether, 2,2,4-trimethylpentylglycidyl ether, phenyl glycidyl ether,cresyl glycidyl ether or glycidyl esters, may be added to the curablemixtures for reducing the viscosity.

The mixtures according to the invention may furthermore contain, asfurther customary additives, extenders, fillers and reinforcing agents,such as, for example, coal tar, bitumen, textile fibres, glass fibres,boron fibres, carbon fibres, mineral silicates, mica, quartz powder,hydrated aluminium oxide, bentonites, wollastonite, kaolin, silicaaerogel or metal powders, e.g. aluminium powder or iron powder, andfurthermore pigments and dyes, such as carbon black, oxide dyes andtitanium dioxide, flameproofing agents, thixotropic agents, flow controlagents, such as silicones, waxes and stearates, some of which are alsoused as mould release agents, and antioxidants and light stabilizers.

The preparation of the mixtures according to the invention can becarried out in a customary manner by mixing the components with the aidof known mixing units (stirrers, rolls).

The B-stage curing of the compositions according to the invention isgenerally effected by exposure to light of suitable wavelength at roomtemperature or slightly elevated temperature. As a rule, an exposuretime of less than one minute is sufficient.

However, it is also possible to initiate the B-stage curing thermallywhen suitable thermal free radical formers are used.

The complete crosslinking with shaping (C-stage curing) is effectedpreferably at above 80° C., for example at 80–200° C., in particular atabout 100–180° C., for about 20–60 minutes.

The crosslinked systems have excellent mechanical and thermalproperties, even if complete curing is carried out only after relativelylong storage (several weeks to months) of the curable mixtures or of theB-stage.

As mentioned, the mixtures according to the invention are suitable inparticular as impregnating resins for the production of fibre compositematerials. The invention thus also relates to a process for thepreparation of prepregs, characterized in that a reinforcing material isimpregnated with a composition according to claim 1 and is exposed toactinic radiation until the material solidifies by photopolymerizationof the photopolymerizable compound (d) to give a substantially solidlayer.

Preferred reinforcing materials are glass fibres and carbon fibres.

EXAMPLE 1

A. Preparation of the Resin/Curing Agent Mixture

A mixture of 3.03 g of Hycar® ATBN 1300×21 (amine-terminatedbutadiene/acrylonitrile copolymer; Noveon Inc., USA), 1.86 g ofphenylimidazole, 5.57 g of benzylamine, 2.78 g of1,1′-(4-methyl-m-phenylene)bis(3,3′-dimethylurea), 4.63 g ofdicyandiamide and 1.16 g of benzyl alcohol is homogenized under yellowlight by means of a three-roll mill and then added to a mixture of 41.58g of bisphenol A diglycidyl ether (epoxide content 5.45–5.56 eq/kg),22.39 g of bisphenol A diglycidyl ether (epoxide content 1.9–2.0 eq/kg),9.86 g of cresol glycidyl ether (epoxide content 5.3–5.7 eq/kg), 6.82 gof dipentaerythrityl pentacrylate, 0.24 g of2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one and 0.08 g ofisopropylthioxanthone.

B. Preparation of the Prepreg

A woven glass fabric is impregnated with the resin mixture on apolypropylene film at room temperature (RT). In order to remove the airand to distribute the binder optimally, a glass rod is rolled over theprepreg; the resin content is 40%. In order to reach the B-stage, theprepreg is exposed on both sides in succession for 10–40 seconds to a 7300 W metal halogen mercury vapour lamp (1 500–2 000 mJ/cm²). Theprepregs thus obtained are slightly tacky.

Flow after storage of the prepreg (1 to 3 days at RT): 17–20%.

The prepregs are then pressed to give a laminate (130° C./5 min).

T_(g)=80° C.

Flexural strength test according to ISO 178/93:

Modulus of elasticity=24 700 MPa

Elongation at break=1.44%

EXAMPLE 2

A. Preparation of the Resin/Curing Agent Mixture

A mixture of 1.64 g of phenylimidazole, 4.92 g of benzylamine, 1 g of2,4,6-tris(dimethylaminomethyl)phenol, 68.07 g of bisphenol A diglycidylether (epoxide content 5.45–5.56 eq/kg), 20 g of cresol glycidyl ether(epoxide content 4.25 eq/kg), 4.1 g of dipentaerythrityl pentacrylate,0.2 g of 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one and0.07 g of isopropylthioxanthone is prepared under yellow light.

B. Preparation of the Prepreg

A woven glass fabric is impregnated with the resin mixture on apolypropylene film at room temperature (RT). In order to remove the airand to distribute the binder optimally, a glass rod is rolled over theprepreg. To reach the B-stage, the prepreg is exposed on both sides insuccession for 10–40 seconds to a 7 300 W metal halogen mercury vapourlamp (1 000–2 000 mJ/cm²). The prepregs thus obtained are slightly tackyand have a dry surface after about 2–3 hours at RT. The prepregs arestable for at least 5 days at RT.

The prepregs are then pressed to give a laminate (130° C./5 min).

Flexural strength test according to ISO 178/93:

-   Modulus of elasticity=29 000 MPa-   Elongation at break=3.1%

1. Composition containing (a) a liquid epoxy resin, (b) an aliphatic orcycloaliphatic primary monoamine and/or an aliphatic or cycloaliphaticdisecondary diamine, (c) a latent curing agent for the epoxy resin (a)which does not react until temperatures above 70° C. (measured by meansof DSC at a heating rate of 10° C./min), (d) a photopolymerizablecompound and (e) a photoinitiator, the ratio of the number ofequivalents of epoxy groups to that of photopolymerizable groups being1:0.01 to 1:0.07 and wherein the composition contains 0.25–0.75aminehydrogen equivalent of the component (b) per epoxide equivalent ofthe epoxy resin (a).
 2. Composition according to claim 1, containing abisphenol diglycidyl ether or an epoxy novolak as component (a). 3.Composition according to claim 1, containing bisphenol A diglycidylether or an epoxycresol novolak as component (a).
 4. Compositionaccording to claim 1, containing a primary monoamine as component (b).5. Composition according to claim 1, containing benzylamine,n-octylamine, 2-phenylethylamine, 3-(2-ethylhexyloxy)propylamine or2-(2-aminoethoxy)ethanol as component (b).
 6. Composition according toclaim 1, containing diaminodiphenylsulphone, dicyandiamide,phenylimidazole and 2,4,6-tris(dimethylaminomethyl)phenol as component(c).
 7. Composition according to claim 1, containing an acrylic acidester or a methacrylic acid ester as component (d).
 8. Compositionaccording to claim 1, containing ethylene glycol dimethacrylate,1,4-butanediol dimethacrylate, 2-hydroxyethyl methacrylate,2-hydroxypropyl methacrylate, 2-ethoxyethyl methacrylate,1,1,1-trimethylolpropane trimethacrylate, pentaerythritol tetraacrylateor dipentaerythritol pentacrylate as component (d).
 9. Compositionaccording to claim 1, containing isopropylthioxanthone or2-methyl-1-[4-(methylthio) phenyl]-2-morpholinopropan-1-one as component(e).